standards were primarily directed toward the user-network interface. This allowed many vendors to begin participating in the development of ISDN equipment such as: switches, terminals, as well as an assortment of VLSI chips for ISDN. The evolution of ISDN technology is occurring at a rapid pace. Throughout the world ISDN has undergone many trials, and is actually in small scale operation in West Germany. Within the next year several other countries are expected to make ISDN services available to large customers. The United States is lagging behind other nations in the implementation of ISDN because unlik-other countries, the U.S. does not have a centralized provider of communications. The European countries have government controlled Postal, Telephone, and Telegraph companies (PTT's). Within the United States there is heavy competition between companies (AT&T, GTE, Northern Telecom, etc.) for the ISDN market and therefore these companies are unwilling to take big financial risks during the early stages of ISDN development. Despite this cautious approach taken by U.S. companies, there are several field trials currently being conducted across the U.S., and customers in the U.S. can expect an operational ISDN within the next two or three years. The initial ISDN customers will be large companies, and as ISDN matures and becomes more economical the market will expand into use by small companies and will eventually migrate into use by .rI

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